Kim Jong Un has agreed to hold a second summit with US President Donald Trump as soon as possible, Seoul said Sunday, after Washington's top diplomat held "productive" talks on denuclearisation with the North Korean leader in Pyongyang.

Declaring a formal end to the Korean War now is the best option for the US to accelerate North Korea’s denuclearisation process and avoid repeating the mistakes of its past administrations, according to a prominent North Korea expert.

The governments of Japan and Russia held a meeting of their foreign and defence ministers – the so-called two-plus-two talks – in Moscow. In addition to their accord on a policy of cooperating toward North Korea’s denuclearisation, the two countries agreed to hold vice-ministerial-level meetings on security issues on a regular basis.

The US will urge the international community to keep up sanctions pressure against North Korea at a security forum in Singapore this week, as concerns mount that Pyongyang has made little progress towards denuclearisation.

US Secretary of State Mike Pompeo was en route to Pyongyang Friday to press Kim Jong Un for a more detailed commitment to denuclearisation following the North Korean leader's historic summit with President Donald Trump.

Firmly maintaining the allied relationship to prepare for contingencies while promoting the denuclearisation of North Korea and easing of tensions has been confirmed by both the United States and South Korea. This is of no small significance.

The United States believes it has North Korean leader Kim Jong-un’s commitment to completely dismantle his country’s nuclear weapons, while denuclearisation would definitely be verified, a senior US security official said on Monday.

North Korea's Kim Jong Un understands that denuclearisation must happen "quickly", US Secretary of State Mike Pompeo said Thursday, warning there will be no sanctions relief for Pyongyang until the process is complete.

Thailand’s Foreign Ministry has welcomed Tuesday’s historic meeting between the US President Donald Trump and North Korea Supreme Leader Kim Jong-un as landmark towards the denuclearisation of the Korean Peninsula.